Marie Tharp

Marie Tharp, an oceanographic cartographer who drew pioneering maps of the world's oceans and whose observations from the late 1950s through the 1970s helped scientists reconsider the geology of the seafloor, has died. She was eighty-six.

Tharp was born July 30, 1920, in Ypsilanti, Michigan, into a mapmaking family. Her father, William, was a surveyor who made soil classification maps for the U.S. Department of Agriculture. Following advice to find something to do that she loved, Tharp earned a bachelor's in English and music, with four minors, from Ohio University in 1943; a master's in geology from the University of Michigan; and a degree in mathematics from the University of Tulsa while working as a geologist for an Oklahoma oil company.

She moved to New York in 1948 and joined Columbia's geology department as a research assistant. Bruce Heezen, who would later be her collaborator on revolutionary sea floor maps, arrived two weeks later.

Mapping the vast, hidden seafloor was "a once-in-the-history-of-the-world opportunity" for anyone, but especially for a woman in the 1940s, Tharp recalled decades later. She had been recruited to study geology at the University of Michigan only because so many men were in the military during World War II. Because women weren't allowed to sail on research ships in the 1940s and '50s, Tharp remained behind, painstakingly plotting sonar readings of the ocean floor often sent back by Heezen, a marine geologist with whom she spent three decades in a personal and professional partnership.

Over five years, as she pieced together a puzzle of the North Atlantic Ocean, an enormous mountain range with a puzzling peculiarity took shape. What became known as the Mid-Atlantic Ridge showed signs of a crack down the middle that led Tharp to conclude that the seafloor was spreading, a radical notion at the time.

Her early observations and maps encouraged scientists to reexamine the theory of continental drift: the belief that the continents once had been one giant land mass that was slowly pulled apart through the movement of tectonic plates. Their work expanded to include the South Atlantic, Indian, Arctic, Antarctic, and Pacific oceans. It culminated with the map of the world's oceans, published weeks after Heezen died of a heart attack on a research expedition in 1977.

After retiring, Tharp ran a map-distribution business in South Nyack, New York, and wrote several articles on Heezen's life.